Pulse tube refrigerating systems for producing cryogenic temperatures are known. For example, as described in Ishizaki et al., U.S. Pat. No. 5,269,147, incorporated by reference herein, a working fluid contained within a tube is compressed adiabatically by the introduction of pressurized fluid into the tube causing an increase in the temperature of the working fluid. Working fluid which has been compressed passes to a heat exchanger to transfer heat into the atmosphere. The pressurized fluid is then allowed to flow from the tube and working fluid returns to the tube and expands to decrease in temperature. The cooled working fluid passes to a refrigerating section where it is available as a coolant. The compression and expansion cycle is repeated.